Reaction of early transition metal complexes with macrocycles. II. Synthesis and structure of TiCl3(H2O) · 18-crown-6, a compound with a unique bidentate bonding mode for the 18-crown-6 molecule

18-crown-6 reacts with TiCl₃ in CH₂Cl₂ to form a complex in which the crown ether functions as a tridentate ligand. Addition of moist hexane affords a molecular complex in which the crown ether functions as a bidentate ligand. A water molecule is bonded directly to the titanium atom and is further hydrogen bonded to three of the oxygen atoms of the crown. The deep blue crystals of the CH₂Cl₂ adduct belong to the monoclinic space groupP2₁/n witha=13.481(8),b=8.021(5),c=21.425(9) Å, =97.32(5)°, and _calc = 1.51 g cm^–3 forZ=4. Refinement led to a conventionalR value of 0.040 based on 873 observed reflections. The Ti–O bond distances for the crown oxygen atoms are 2.123(8) and 2.154(9) Å, while the oxygen atom of the water molecule is bonded at 2.072(8) Å. The octahedral coordination sphere of the titanium atom is completed by the three chlorine atoms at distances of 2.340(5), 2.352(4), and 2.373(4) Å. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82034 (10 pages).     

Physical and Chemical Properties of Dissolved Electrons (Excess Electrons)

Electrons produced in a gaseous, liquid, or solid solvent are called dissolved electrons or excess electrons. These excess electrons can exist as quasi-free particles of high mobility in a delocalized state, comparable with electrons in a metal; or as bound particles of low mobility they can be localized within narrow limits—in a solvent cavity formed by repulsive forces. Localized electrons can also be solvated like normal ions. Characteristically, such solvated electrons exhibit broad and extensive absorption spectra in the visible to near infrared spectral range. The localized and delocalized states of the excess electrons can be in equilibrium with each other, such that a continuous transition of the properties between the limiting extremes can be observed. The reactions of the excess electrons with suitable acceptors (substrates) are initiated by an attachment-detachment equilibrium A + e^? ? A^? which is followed by further chemical rearrangements. The rate constants of these reactions vary by more than 15 powers of ten depending on the substrates and the solvents. Most of the properties of excess electrons in solution can be interpreted by means of a model which is easily understandable but quantitatively evaluated only with considerable effort.     

Breakthrough of polymers in interactive liquid chromatography

Two separate peaks are observed for narrow polymer standards in both isocratic and gradient HPLC. One peak appears around the solvent front (the "solvent-plug peak" or "breakthrough peak"), whereas the second peak is retained significantly--or even highly. Although the effect has been observed many times before, it has never been rigorously explained. In this paper we provide a detailed explanation for the breakthrough peak. The two completely separate peaks are demonstrated not to represent to different fractions of the sample (e.g., the low- and high-molecular-mass parts of the distribution). Both peaks are representative of the entire polymeric sample for narrow polymer standard. Because the amount of the polymer in the breakthrough peak may vary, the quantitative analysis of the polymers by LC is jeopardized. The effects of the sample solvent, the (initial) mobile phase composition, the injection volume, the injected sample concentration, the column temperature, and the analyte structure and molecular mass on the breakthrough peak were investigated in LC experiments involving standards of polystyrene and poly(methyl methacrylate). Three necessary and sufficient conditionsare suggested for the breakthrough phenomenon to be observed. Recommendations to avoid the breakthrough phenomenon are given, culminating in a structured method for selecting the best possible sample solvents.     

Synthesis and functional studies of THF-gramicidin hybrid ion channels

THF-gramicidin hybrids 2-4 with the L-THF amino acid 1 in positions 11 and 12 and compounds 5-8 with the D-THF amino acid ent-1 in positions 10 and 11 were synthesized and their ion channel properties were studied by single-channel-current analysis. The replacement of positions 11 and 12 by the L-THF amino acid 1 gave a strongly reduced channel performance. In contrast, replacement of positions 10 and 11 by the D-THF amino acid ent-1 gave rise to new and interesting channel properties. For the permeability ratios, the ion selectivity shifts from Eisenman I towards Eisenman III selectivity and the channels display ms-dynamics. Most remarkable is the asymmetric compound 8, which inserts selectively into a DPhPC membrane and displays voltage-directed gating dynamics.     

The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene,syntheses, photolyses,X-ray-structure analysis,and PE spectra

The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I₁ = 8.0₀, I₂ = 9.0₅ eV; 2 ; I₁ = 8.0₀, I₂ = 9.2₅eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond.     

Na5AlF2(PO4)2: Darstellung,Kristallstruktur und Ionenleitfähigkeit

Na₅AlF₂(PO₄)₂: Synthesis, Crystal Structure and Ionic Conductivity Two different procedures (precipitation from aqueous solution and solid state reaction) for the synthesis of hitherto unknown Na₅AlF₂(PO₄)₂ were optimized. The crystal structure was determined using diffractometer data (P3 , a = b = 10.483(1), c = 6.607(1) Å, MoKα, 1080 independent reflections, R_w = 0.025). PO₄-tetrahedra and AlO₄F₂-“octahedra” are connected via common vertices forming a twodimensionally extended heteropolyanion. Sodium is located in interconnected spacings of the [AlF₂(PO₄)₂]-part of the structure. Ionic conductivity as expected because of these structural features was affirmed experimentally.     

A structure refinement of the high pressure modification BaI2-II

A high pressure phase BaI₂-II, which can be quenched and retained as a metastable form at ambient conditions, is reported. The structure has been determined by X-ray investigations using single crystals. BaI₂-II crystallizes in an anti-Fe₂P-type arrangement, space group $\text{P}\text{6}\text{2m, a = 9.142(6)}$Å, c = 5.173(3)Å, which is slightly denser than the PbCl₂-type structure found at normal pressure. Structural features of the two phases are discussed in comparison.     

Inkjet printing of well-defined polymer dots and arrays

Inkjet printing represents a highly promising polymer deposition method, which is used for, for example, the fabrication of multicolor polyLED displays and polymer-based electronics parts. The challenge is to print well-defined polymer structures from dilute solution. We have eliminated the formation of ring stains by printing nonvolatile acetophenone-based inks on a perfluorinated substrate using different polymers. (De)pinning of the contact line of the printed droplet, as related to the choice of solvent, is identified as the key factor that determines the shape of the deposit, whereas the choice of polymer is of minor importance. Adding 10 wt % or more of acetophenone to a volatile solvent (ethyl acetate)-based polymer solution changes the shape of the deposit from ring-like to dot-like, which may be due to the establishment of a solvent composition gradient. Arrays of closely spaced dots have also been printed. The size of the dots is considerably smaller than the nozzle diameter. This may prove a potential strategy for the inkjet printing of submicrometer structures.     

Evaluation of a new multiple-layer spotting technique for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of synthetic polymers

A new multiple-layer matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) sample-spotting technique is described. This fast and easy technique was evaluated with poly(ethylene glycol) (PEG) standards and optimized conditions for these synthetic polymers were obtained. PEGs up to 35 kDa were detectable with this approach and single monomer resolution was observed up to 20 kDa. The spotting was performed using a multiple-layer approach, which offers the capability of complex sample preparation without the requirement of premixing the different matrix, analyte and doping salt solutions. The technique reduces the time required for sample preparation and offers high flexibility with respect to sample composition and solvents utilized for the crystallization of the compounds. The technique is thus perfectly suited for applications in combinatorial material research.     

Stille Cross‐Coupling of a Racemic Planar‐Chiral Ferrocene and Crystallographic Trace Analysis of Catalysis Intermediates and By‐products

A pressure‐controlled procedure for the S_N1 reaction of rac‐1‐[(dimethylamino)methyl]‐2‐(tributylstannyl)ferrocene ( 1 ) to rac‐1‐(phthalimidomethyl)‐2‐(tributylstannyl)ferrocene ( 2 ) was developed. Pd⁰‐Catalyzed Stille coupling of 2 with iodobenzene afforded rac‐1‐phenyl‐2‐(N‐phthalimidomethyl)ferrocene ( 5 ) in 74% yield; after trace enrichment by crystallization of the combined mother liquors, one single crystal of each, 5 , catalysis intermediate trans‐iodo(σ‐phenyl)bis(triphenylarsino)palladium(II) ( 7 ), trans‐diiodobis(triphenylarsino)palladium(II) ( 8 ), and rac‐2,2′‐bis(phthalimidomethyl)‐1,1′‐biferrocene ( 9 ) could be isolated by crystal sorting under a microscope and characterized by X‐ray crystal structure analysis. Furthermore, 5 was deprotected to amine ( 11 ), which does even survive the Birch reduction to rac‐1‐(aminomethyl)‐2‐(cyclohexa‐2,5‐dienyl)ferrocene ( 12 ).